The present invention relates to a method for fabricating a micro machine, more specifically to a method for fabricating a micro machine having a torsion bar.
Micro machines using micromachining are recently much noted. In micro machines, swinging members are supported by, e.g., torsion bars, that is, torsion bar springs.
FIGS. 25A to 28D are sectional views of a proposed optical switch having a torsion bar in the steps of a method for fabricating the proposed optical switch, which show the method.
First, as shown in FIG. 25A, a silicon substrate 106 and a silicon substrate 168 are bonded to each other with a silicon oxide film 118 therebetween. Then, a metal film 168 is formed on the entire surface of the silicon substrate 106.
Next as shown in FIG. 25B, the metal film 168 is patterned. Then, a mirror 124 and a bump 172 are formed of the metal film 168.
Then, as shown in FIG. 25C, silicon oxide films 174, 166 are formed respectively on the upper surface of the silicon substrate 106 and the under surface of the silicon substrate 108.
Next, as shown in FIG. 25D, the silicon oxide film 174 is patterned by photolithography.
Then, as shown in FIG. 26A, the silicon oxide film 166 is patterned by photolithography.
Then, as shown n FIG. 26B, a metal film 160 is formed on the under surface of the silicon substrate 108.
Next, as shown in FIG. 26C, the metal film 160 is patterned. Thus, a bump 164 is formed of the metal film 160.
Next, as shown in FIG. 26D, a photoresist film 100 is formed on the silicon substrate 106. Then, the photoresist film 100 is patterned by photolithography.
Then, as shown in FIG. 27A, with the photoresist film 100 as a mask, the silicon substrate 106 is etched. Thus, steps 101 are formed on the silicon substrate 106.
Next, as shown in FIG. 27B, the photoresist film 100 is removed.
Then, as shown in FIG. 27C, a photoresist film 102 is formed on the under surface of the silicon substrate 108. Then, the photoresist film 102 is patterned by photolithography.
Then, as shown in FIG. 27D, with the photoresist film 102 as a mask, the silicon substrate 108 is etched. Thus, steps 103 are formed on the silicon substrate 108.
Then, as shown in FIG. 28A, the photoresist film 102 is removed.
Next, as shown in FIG. 28B, with the silicon oxide film 174 as a mask, the silicon substrate 106 is etched, retaining the steps 101. Thus, a movable electrode 112 having a digital portion 112a of the silicon substrate 106 is formed while a spring portion 120a of the silicon substrate 106 is formed.
Then, as shown in FIG. 28C, with the silicon oxide film 166 as a mask, the silicon substrate 108 is etched, retaining the steps 103. Thus, a stationary electrode 110 having a digital portion 110a of the silicon substrate 108 is formed while a spring portion 120b of the silicon substrate 108 is formed.
Then, as shown in FIG. 28D, the silicon oxide films 174, 166, 118 are etched off. Thus, the micro machine having the torsion bar 116 which comprises the spring portion 120a and the spring portion 120b is fabricated.
However, in the method for fabricating the proposed micro machine as shown in FIGS. 25A to 28D, wherein the silicon substrate 106, 108 is etched, retaining the steps 101, 103 to thereby form the spring portions 120a, 120b constituting the torsion bar 116, it is very difficult to control the thickness and shape of the spring portions 120a, 120b forming the torsion bar 116. Accordingly, the method for fabricating the proposed micro machine makes the yields low.